THURSDAY, April 2, 2015 (HealthDay News) -- If you're on the verge of developing diabetes, parking yourself in front of the TV might be one of the worst things you could do for your health, a new study suggests.

Every extra hour a person with prediabetes spends watching TV each day raises their risk of developing full-blown type 2 diabetes by 3.4 percent, according to research published April 1 in the journal Diabetologia.

The study couldn't prove cause-and-effect. But the increased risk associated with being a couch potato occurred whether or not the study participants were taking diabetes drugs, or whether or not they were eating healthy diets and exercising, the researchers found.

However, people who tried to prevent diabetes through healthy lifestyle changes did end up watching less television over time, the study found.

The results are troubling, given the epidemic of obesity that continues to plague the United States, said senior study author Andrea Kriska, a professor of epidemiology at the University of Pittsburgh's Graduate School of Public Health.

"As time goes on and people are getting less active and more overweight, the number of people at risk for diabetes is increasing by leaps and bounds. It's not a rare group of people" who will be exposed to increased diabetes risk due to their sedentary habits, Kriska said.

The new study relies on data from participants in the Diabetes Prevention Program, a federally funded study published in 2002. That study included slightly more than 3,200 overweight U.S. adults between 1996 and 1999. The study's goal was to delay or prevent type 2 diabetes in high-risk patients, either with the diabetes drug metformin or via lifestyle changes.

Eating right and engaging in physical activity proved the most successful route, resulting in a 58 percent decrease in the development of diabetes compared to doing nothing. By comparison, metformin caused only a 31 percent decrease in diabetes development, Kriska said.

Since they'd proven that physical activity can forestall diabetes, researchers decided to take the opposite tack and explore whether sitting around for extended periods can raise diabetes risk, said study author Bonny Rockette-Wagner, director of physical activity assessment at the University of Pittsburgh's Graduate School of Public Health.

Prior research has indicated that long periods spent sitting motionless can have negative effects on metabolism, Rockette-Wagner explained.

"If you think about it, we all recognize the fact that when we sleep our bodies are at rest, and everything sort of slows down," she said. "When we're sitting for long periods of time, our body also starts to slow down. It might not be in a sleeping state, but it goes into a more rested state and things start to slow down."

Prior to the study, participants in the Diabetes Prevention Program all spent the same amount of time watching TV, an average of 140 minutes per day.

But people engaging in lifestyle changes ended up reducing their TV time by 22 minutes a day over the course of the study. By comparison, people taking metformin reduced their TV watching by just 3 minutes a day, and those following no plan at all watched 8 minutes fewer per day.

The researchers then investigated the impact of sedentary behavior over time on diabetes incidence. For participants in all three groups, the risk of developing diabetes increased approximately 3.4 percent for each hour spent watching TV, after the researchers adjusted for other variables.

In addition to the impact on metabolism, sitting for long periods in front of the TV also can promote overeating, noted David Marrero, president of health care and education for the American Diabetes Association.

"I know when I'm sitting around watching TV, I'm more likely to graze and eat crappy food," Marrero said. "When people are watching passively, there's a tendency to snack. When's the last time you measured out a portion size of potato chips and ate it in front of the television?"

This increased risk from TV watching might not apply to healthy people who are not at high risk for diabetes, Kriska and Rockette-Wagner added.

They noted that the Diabetes Prevention Program specifically focused on people who were overweight and prediabetic.

"Not everyone in the general population would be at high risk," the researchers said. "We would hypothesize that the risk increase from TV watching may be lower in those not at high risk for diabetes, but obviously could not test that in our study population."